Mold used in manufacture of drill bits and method of forming same

ABSTRACT

A mold usable to form a drill bit body and a method for forming such a mold are disclosed. A shell is provided, the shell having a cavity. Fusible material, such as foundry sand, is provided into the cavity, then fused to form a solid insert within the shell. The solid insert is then modified, such as by machining, to form a mold having features usable to form a drill bit body having desired characteristics. Materials for forming the drill bit body can then be provided into the mold, for heating and cooling. Then, the drill bit body and mold can be removed from the shell. The shell is thereby reusable, while the mold, being formed from inexpensive fusible materials, can be removed or destroyed, if necessary, to free the drill bit body.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part application which claims priority to the copending U.S. patent application having Ser. No. 12/288,889, filed Oct. 24, 2008, the entirety of which is incorporated herein by reference.

BACKGROUND OF INVENTION

The present invention relates, generally, to the manufacture of drill bits usable to drill oil and gas wells.

Various types of drill bits have been developed and found useful in different drilling environments. Bits typically used for drilling boreholes in the oil and gas industry include roller cone bits and fixed cutter bits. Cutting structures on bits vary depending on the type of bit and the type of formation being cut. Roller cone cutting structures typically include milled steel teeth, tungsten carbide inserts, or diamond enhanced inserts. Cutting structures for fixed cutter bits typically include polycrystalline diamond compacts, commonly referred to as “PDC” cutters. The selection of a bit type and cutting structure for a given drilling application depends on many factors including the formation type to be drilled, rig equipment capabilities, and the time and cost associated with drilling.

Fixed cutter drill bits, also referred to as fixed head bits or drag bits, are generally more expensive than mill tooth roller cone drill bits and are considered to offer less aggressive cutting structures than roller cone drill bits. However, in several applications, fixed cutter bits can be used to drill longer well segments in a single run and can be rebuilt and reused multiple times to provide an overall economic benefit that outweighs the higher cost. Fixed cutter bits which include PDC cutters are typically referred to as PDC bits.

It is common in the art of manufacturing PDC, fixed cutter drill bits, to manufacture the body of the drill bit using a graphite mold. Conventional molds are typically manufactured as a single piece of machined graphite. Graphite is used primarily due to the ability to readily machine the material to provide mold features, and due to the low coefficient of expansion, and uniformity of expansion, of the material when exposed to high heat during the drill bit molding process.

In use, a conventional graphite mold is first machined to provide desired features to the mold for forming a drill bit body having selected characteristics. For example, features usable to provide a drill bit body with nozzles, a bore, blades and/or lugs, junk slots, pockets for containing PDC cutters, and other drill bit elements known in the art can be provided to a mold for formation of a drill bit body having such elements. The drill bit body is then formed through a powdered metal infiltration casting method, which includes packing the mold with a powdered metal matrix material, such as tungsten carbide, then providing pieces of a metal or alloy to be used as a binding material above the packed mold, often in a separate chamber provided with a bore, funnel, or similar member used to allow molten metal to flow into the packed mold. The mold is then heated in a furnace to a temperature sufficient to melt the binding material, typically at or in excess of 2000 degrees Fahrenheit, such that the molten binding material is drawn into the spaces between particles of the packed powdered metal matrix material through capillary action. Once cooled through a controlled process, the binding material hardens between matrix particles to form the drill bit body. To remove the drill bit body from the mold, the mold must then be physically broken, such as by striking the mold with a hammer or similar implement.

FIG. 1 of the drawings illustrates a conventional, prior art, single piece graphite mold usable to manufacture a body for a drill bit.

Due to the expense of large, single piece graphite molds, it has become desirable to minimize the quantity of graphite required to produce a drill bit body. Copending U.S. patent application Ser. No. 12/288,889 describes use of a two-piece mold that includes a reusable graphite shell sized to contain interchangeable graphite molds. The use of the two-piece mold also enables the manufacture of several sizes of drill bit bodies using a single reusable mold shell, thus reducing the quantity of graphite used to produce each drill bit body. However, the materials, time, equipment, and labor necessary to produce graphite molds carry a significant cost, ranging from $500 to $5000 per mold, or more.

As such, a need exists for apparatuses and methods usable to form drill bit bodies that incorporate use of less expensive materials that are more easily machined or otherwise manipulated when compared to graphite.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a pictorial, isometric view of a conventional, prior art, single piece graphite mold used for manufacturing a drill bit body;

FIGS. 2A, 2B and 2C respectively illustrate an exploded view of a mold usable in accordance with an embodiment of the present invention;

FIG. 3A illustrates an assembled view of the elements illustrated in FIGS. 2A, 2B and 2C;

FIG. 3B is a schematic view, partially in cross section, illustrating the assembled mold;

FIG. 4A is an elevated, schematic view, in cross section, illustrating an embodiment of the assembled mold;

FIG. 4B is a top plan, schematic view of the embodiment illustrated in FIG. 4A with the top portion of FIG. 4A removed;

FIG. 5 is a side view, in cross section of the mold shell illustrated in FIG. 2A;

FIG. 6 is a side view, in cross section, illustrating the mold core illustrated in FIG. 2B;

FIG. 7 is a pictorial, isometric view of an embodiment of the assembled mold; and

FIG. 8 illustrates the equipment used in milling the drill bit within the mold while resting on a fixture to support the mold core.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention relates, generally, to methods for forming a mold usable to create a drill bit body, and subsequent use of the mold to manufacture the drill bit body. While conventional methods for forming a drill bit body include use of graphite molds, embodiments of the present invention incorporate use of an inexpensive, fusible material, such as foundry sand or a similar mixture of silica, binders, resins, plasticizers, and/or polymers, which can be mixed, heated, or otherwise fused to form a solid insert within a generally rigid shell. Typical varieties of resin-bonded foundry sand usable within the scope of the present invention include fine sand particles, each coated with a thin layer of resin, which can be heated to approximately 250 to 450 degrees Fahrenheit to cause the resin to at least partially melt, thereby causing the particles of sand to adhere together to form a solid insert within the shell.

A solid insert formed in such a manner from fused foundry sand or a similar fusible material is more easily machined or otherwise modified than conventional graphite molds, enabling a mold for forming a drill bit body having desired characteristics to be created more efficiently than conventional methods, using less costly materials. Machining of the solid insert can be performed within the shell, without requiring removal of the fused material, however in an embodiment of the invention, the solid insert can be removed from the shell to facilitate precise modifications and/or use of specific equipment to form the mold.

Additionally, materials such as foundry sand are very friable, enabling the mold to be easily removed from the shell, such that the shell can be reused. The heat applied through the drill bit molding process, which can exceed 2000 degrees Fahrenheit, can destroy the remaining resin or other binding component of the fusible material, such that after the drill bit body has been molded, the fusible material will simply fall away from the drill bit body when the drill bit body is removed from the mold, reducing the time and labor normally required to destroy a conventional graphite mold.

This feature substantially reduces manufacturing and material costs when compared with conventional methods, as a graphite mold can require a significant expense, while foundry sand or a similar material can cost as little as $0.50 per pound, or less. The relatively inexpensive nature of the fusible mold material of the present invention and the comparative ease with which it can be machined or milled to form molds reduces the loss incurred when a mold is destroyed after use, or otherwise discarded. However, it should also be noted that when desired, molds formed from fusible material can be recovered intact and reused.

The present invention thereby provides a hybrid molding method for forming a drill bit body that incorporates use of a reusable shell formed from a generally rigid material, such as graphite, having an interior that can be provided with an inexpensive, easily-machined, fusible material, such as foundry sand, which is usable to form a mold. Conventional sand-molding processes, such as those used in foundries, are unsuitable for use with most matrix materials desirable for formation of drill bit bodies due to the weight of such materials. For example, a quantity tungsten carbide has a weight of approximately 2.5 times that of an equal quantity of steel. Use of a hybrid mold containing fusible material within a generally rigid shell provides sufficient strength for containing powdered matrix materials and binding metals, while minimizing the time and expense required to utilize conventional graphite molds.

Embodiments of the invention contemplate that use of a mold formed from foundry sand or a similar fusible material can provide drill bit bodies with generally rough finishes, which can be machined after molding. However, the interior of the mold can be provided with a mixture of clay and graphite powder, such as that used to repair cracks in conventional graphite molds, or a similar material that will melt under the high heat of the molding process. The presence of the liquid clay mixture within the mold results in the formation of drill bit bodies having an exceptionally smooth finish, superior to that obtained through use of conventional graphite molds. In further embodiments of the invention, selective regions of the mold can be provided with a mixture of clay and graphite powder or a similar material, such that desired regions of the formed drill bit body are provided with a smooth finish, while other regions, such as pockets for containing PDC cutters, are provided with a rough finish, which would enable a more secure bond to be formed between the drill bit body and one or more cutter elements through a brazing process.

Referring now to FIG. 1, a pictorial, isometric view of a single piece, prior art graphite mold, known in the art, is shown. The depicted mold (10) is generally usable to form PDC drill bits. The mold (10) is shown having a lower portion (12) and an upper ring (14), the upper ring (14) containing a cavity used as the mold for manufacturing a PDC drill bit body. In use, the depicted mold (10) is partially filled with a tungsten carbide powder to which a metal alloy is applied. Upon heating, the alloy mixes with the molten tungsten carbide to form a matrix, which assumes the shape of the mold (10) to form a drill bit body (18).

After formation of the drill bit body (18), a milling process can be performed to mill various components of the drill bit body to form the finished product. FIG. 8 depicts an embodiment of this process, in which a milling device (16) is usable to mill portions of the drill bit body.

Following formation of a drill bit body using the single piece mold (10) of FIG. 1, the mold (10) is generally removed from the drill bit body (18) by physically breaking the mold (10), such as through use of a hammer or similar implement. As a result, the conventional molding process incurs a substantial quantity of waste, as the broken mold cannot be reused. Additionally, imprecise breaking of the mold (10) can potentially cause damage to the drill bit body (18).

Referring now to FIGS. 2A, 2B, and 2C, there is illustrated a mold shell (30) having a cavity (34) therein. The mold shell (30) can be formed from any generally rigid material able to withstand the molding process, such as graphite. FIG. 5 depicts a cross-sectional view of the mold shell (30) and cavity (34). FIG. 2B depicts a mold core (32), sized to closely fit within the cavity (34), enabling the mold core (32) to be easily removed from the mold shell (30) after the molding process has been completed. As a result, the mold shell (30) is not broken to free the drill bit body and can be reused.

The mold core (32) can be formed by providing, into the cavity (34), a fusible material, such as foundry sand or a similar mixture of silica or another structural component with one or more binders, resins, plasticizers, and/or polymer components. The fusible material can then be fused, such as by applying heat using a heating device, or simply through use of a mixing or machining device, to cause fusing of the resins, plasticizers, or other components of the fusible material. After fusing the fusible material, a generally solid insert is formed within the cavity (34), which can be machined, milled, or otherwise modified to form the mold core (32). FIG. 6 depicts a cross-sectional view of the mold core (32), which has been provided with regions for molding nozzles (44) and cutter pockets (46) in a drill bit body.

While the mold core (32) is usable to form a first portion of a drill bit body, other components can be provided above the mold core (32) to form other portions of the drill bit body. For example, FIG. 2C depicts a gauge ring (36), sized to sit on top of the mold shell (30) and surround the cavity, the gauge ring (36) being usable to define the outer diameter of the resulting drill bit body. The gauge ring (36) and other components disposed above the mold shell (30) can be formed from similar, generally rigid materials, such as graphite. In an embodiment of the invention, the gauge ring (36) and similar components can be recovered for reuse.

FIG. 3A depicts an assembled view of the mold shell, mold core, and gauge ring of FIGS. 2A, 2B, and 2C. FIG. 3B depicts a schematic view, partially in cross section, illustrating the assembled mold of FIG. 3A, showing the mold shell (30) disposed about the mold core (32), with the gauge ring (36) positioned above the mold shell (30).

FIG. 4A depicts a cross-sectional, assembled view of the mold shell (30), mold core (32), and gauge ring (36). FIG. 4A also depicts a funnel member (38) disposed above the gauge ring (36), the funnel member (38) being usable to provide drill bit materials, such as tungsten carbide powder, nickel alloys, and other metals and alloys therethrough. Materials provided through the funnel member (38) enter the mold core (32). Heating and subsequent cooling of the drill bit materials thereby forms a drill bit body having a shape defined by the mold core (32) and any other components of the mold, such as the gauge ring (36). Due to the pourable nature of foundry sand and other usable fusible materials, fusible materials used to form the mold core (32) can also be provided through the funnel member (38) into the mold shell (30) without requiring disassembly of the mold.

FIG. 4A also depicts an end cap (42), which can be attached to the top of the funnel member (38), such as through use of a threaded connection. FIG. 4A further depicts, schematically, parts of a drill bit that can be formed through the molding process, described above. Specifically, nozzles (44) and cutter pockets (46) of the resulting drill bit body are shown, which can be milled or otherwise modified, and/or fitted with additional parts or components following the molding process. FIG. 4B illustrates a top plan view of the mold shell, mold core and gauge ring of FIG. 4A, with the end cap removed, such that the funnel member (38) is visible.

FIG. 7 is a pictorial, isometric view of an embodiment of the present mold, depicting a mold core (32) disposed within a mold shell (30). FIG. 7 depicts the mold core (32) having a machined surface used to form various components of a drill bit body. After the molding process, the mold core (32) is easily removable from the mold shell (30), without damaging the mold shell (30). The drill bit body can then be removed from the mold core (32), which in certain embodiments of the invention, can involve breaking of the mold core (32) and/or heating the mold core (32) to cause the fusible material to fall away from the drill bit body during removal. Due to the less costly nature of foundry sand and similar fusible materials, when compared to graphite and other conventional materials, little loss is incurred when a mold core (32) formed from fusible materials must be destroyed.

The present invention thereby provides molds and methods of manufacture that incorporate use of inexpensive fusible materials, avoiding the need for use and destruction of costly graphite molds. The fusible materials of the present invention are more easily machined than conventional mold materials, providing for a more efficient process.

While various embodiments of the present invention have been described with emphasis, it should be understood that within the scope of the appended claims, the present invention might be practiced other than as specifically described herein. 

1. A method for forming a drill bit body, the method comprising the steps of: providing a fusible material into a shell; fusing the fusible material to form a solid insert within the shell; modifying the solid insert to form a mold comprising features usable to form a drill bit body; providing at least one drill bit body material into the mold; heating said at least one drill bit body material, wherein said heated at least one drill bit body material flows into the features of the mold; cooling said at least one drill bit body material to form the drill bit body within the mold; and removing the drill bit body and the mold from the shell.
 2. The method of claim 1, wherein the fusible material comprises a mixture of silica sand and a binder, a resin, a plasticizer, one or more polymers, or combinations thereof.
 3. The method of claim 1, wherein the fusible material comprises foundry sand.
 4. The method of claim 1, wherein the step of fusing the fusible material to form the solid insert comprises heating the fusible material, the generally rigid shell, or combinations thereof.
 5. The method of claim 1, wherein the step of modifying the solid insert to form the mold comprises machining the solid insert, milling the solid insert, or combinations thereof.
 6. The method of claim 1, wherein said at least one drill bit body material comprises tungsten carbide, nickel, monel, steel, cobalt, iron, other transition metals, or combinations thereof.
 7. The method of claim 1, further comprising the step of removing the mold from the drill bit body by breaking the mold, heating the mold to cause disassociation of the fusible material, or combinations thereof.
 8. The method of claim 1, further comprising the steps of removing the mold intact from the drill bit body and inserting the mold into the shell for reuse.
 9. The method of claim 1, further comprising the step of modifying the drill bit body to provide desired features to the drill bit body.
 10. The method of claim 1, further comprising the step of providing an additional material to at least a portion of the mold, wherein the step of heating said at least one drill bit body material causes the additional material to melt whereby a region of the drill bit body is provided with a generally smooth finish.
 11. The method of claim 10, wherein the additional material comprises clay, graphite powder, or combinations thereof.
 12. The method of claim 10, wherein the step of providing the additional material to at least a portion of the mold comprises providing the additional material to one or more cracks, damaged areas, or combinations thereof within the mold to prevent formation of irregularities in the drill bit body.
 13. The method of claim 1, wherein the step of providing said at least one drill bit body material into the mold comprises providing a powdered metal matrix material into the mold and providing one or more metal alloys in fluid communication with the powdered metal matrix material, and wherein the step of melting said at least one drill bit body material comprises melting the one or more metal alloys and permitting the one or more metal alloys to flow into spaces within the powdered metal matrix material.
 14. A mold for forming a drill bit body, the mold comprising: a shell having a cavity; and a removable insert formed from a fusible material, wherein the removable insert comprises features usable to form a drill bit body, and wherein the removable insert can be filled with at least one drill bit body material which when heated and cooled forms a drill bit body comprising the features of the removable insert.
 15. The mold of claim 14, wherein the fusible material comprises a mixture of silica sand and a binder, a resin, a plasticizer, one or more polymers, or combinations thereof.
 16. The mold of claim 14, wherein the fusible material comprises foundry sand.
 17. The mold of claim 14, wherein the shell comprises graphite.
 18. The mold of claim 14, wherein said at least one drill bit body material comprises tungsten carbide, nickel, monel, steel, cobalt, iron, other transition metals, or combinations thereof
 19. The mold of claim 14, further comprising an additional material disposed within at least a portion of the removable insert, wherein the additional material melts when heated such that a region of the drill bit body is provided with a generally smooth finish.
 20. A method for forming a mold usable to manufacture a drill bit body, the method comprising the steps of: providing a shell having a cavity; providing a fusible material into the cavity; fusing the fusible material to form a solid insert within the shell; and modifying the solid insert to form a mold comprising features usable to manufacture the drill bit body.
 21. The method of claim 20, wherein the fusible material comprises a mixture of silica sand and a binder, a resin, a plasticizer, one or more polymers, or combinations thereof.
 22. The method of claim 20, wherein the fusible material comprises foundry sand.
 23. The method of claim 20, wherein the step of fusing the fusible material to form the solid insert comprises heating the fusible material, the generally rigid shell, or combinations thereof
 24. The method of claim 20, wherein the step of modifying the solid insert to form the mold comprises machining the solid insert, milling the solid insert, or combinations thereof 